This invention relates to synthetic circuit components and certain applications for synthetic circuit components that involve improving the frequency response of amplifier circuitry.
From a conceptual point of view, the simplest signal processing task is that of signal amplification. The need for amplification arises because certain “weak” signals, such as those produced by transducers, are frequently too small for reliable detection or processing. Amplifying weak signals increases signal amplitude while preserving the details of the subject waveform, making signal acquisition and additional signal processing feasible.
Currently, circuit designers may choose from a wide variety of amplifier configurations to obtain certain desired performance characteristics. For example, in a communications system, a voltage amplifier may be used to increase the magnitude of a data signal that has become attenuated from traveling across a lengthy transmission line. In a different application, such as a power supply, a current amplifier may be used that provides only a modest amount of voltage gain but substantial current gain. In yet other applications, amplifiers may be chosen for their frequency attributes or for their ability to perform some filtering or shaping of the frequency spectrum.
One characteristic of amplifier circuitry that is often of concern to system designers is frequency response. As a general principle, it is desirable to have the bandwidth of the amplifier be as large as possible so that it may be used in a wide range of applications.
In the past, input networks with large time constants have been utilized to improve the low frequency response of amplifier circuitry (i.e., reliably amplify low frequency signals). An example of a prior art circuit using this technique is shown in FIG. 1. As shown, amplifier circuit 100 includes amplifier 110, coupling capacitor 120, resistor 130 and bias voltage 140. Capacitor 150 represents the parasitic capacitance that often accompanies the input network of amplifier 110. The values of resistor 130 and coupling capacitor 120 are typically selected to minimize jitter and amplitude deterioration experienced when amplifier 110 is required to maintain VOUT at a constant level over a relatively long period of time. This may occur, for example, when a digital communication system is required to produce a long series of logic high signals.
One deficiency of this approach, however, is that such input networks require relatively large components. In the example above, capacitor 120 may have a value of about 33 pF and resistor 130 may have a value of about 1 MΩ. Using components of this size with concomitant parasitic capacitance, tends to limit the bandwidth and increase recovery time of circuit 100 in addition to occupying a significant amount of die space when disposed on an integrated circuit.
Thus, in view of the foregoing, it would therefore be desirable to provide circuits and methods that improve the bandwidth and recovery time of an amplifier. It would also be desirable to provide circuits and methods for reducing the size of the components in an input network of the amplifier.